The present invention relates to a process for manufacturing metal silicide photomask and, more particularly, to a process for manufacturing a metal silicide photomask for use with manufacture of a semiconductor device.
2. Description of the Prior Art
FIGS. 1A to 1D show sequential steps of a metal silicide photomask manufacturing process which is disclosed in co-pending U.S. Application Ser. No. 819,102, filed Jan. 15, 1986, by Watakabe et al., assigned to the same assignee of the present application. First of all, the process of manufacturing a metal silicide photomask will be described with reference to FIGS. 1A to 1D. First, as shown in FIG. 1A, a transparent glass substrate 1, such as silica glass, is prepared and then a metal silicide film 2, such as a titanium silicide, a molybdenum silicide and a tungsten silicide is formed on the transparent glass substrate 1 by means of sputtering process or the like, with a thickness of about 1000 .ANG.. Then, as shown in FIG. 1B, a resist 3 is applied onto the metal silicide film 2, a desired pattern is drawn by light or electron beam and then developing process is achieved, so that a resist pattern can be formed. Thereafter, as shown in FIG. 1C, exposed portion of the metal silicide film 2 is etched away by gas plasma process. For example, if and when molybdenum silicide (MoSi.sub.2) is used as a metal silicide film 2, an etching rate of about 500-1000 .ANG./min is obtained, with a mixed gas of CF.sub.4 +O.sub.2 (2%-20%), vacuum of 0.2 Torr and 300 W. Then, the exposed portion of metal silicide film 2 is etched away, and the resist pattern is removed by means of an oxygen plasma 4, so that a mask pattern of metal silicide is formed, completing the formation of a photomask for use in a process of a semiconductor device.
However, in accordance with the proposed process as described in the foregoing, only a high dry etching-resistant resist can be used and a resist film should be sufficiently thick. Therefore, there is a limitation for very fine patterning, and, if a surface of a metal silicide film is once oxidized, the etching speed becomes slower and hence complete etching may not be achieved.
Incidentally, Japanese Patent Application No. 42176/1981, filed Mar. 23, 1981 and laid open for public inspection Sept. 28, 1982 and Japanese Patent Application No. 42183/1981, filed Mar. 23, 1981 and laid open for public inspection Sept. 28, 1982 disclose that a silicon layer and a metal layer are deposited on a glass substrate so that a pattern of silicide is formed by an electron beam.